Consumer batteries available on the market, such as button cell batteries and zinc-carbon batteries, are generally called primary cells. These batteries are designed to be used once and then discarded. However, heavy metals and electrolytes contained in the primary cells are harmful to the environment, resulting in environmental pollution when they are discarded. For example, if the electrolytes contained in the primary cells leak out, this may cause a chemical reaction with water, which then produces toxic substances.
In recent years, research for alternatives to traditional primary cells has made significant progress. A water-activated power generating device, which is generally known as a water battery, is an alternative to the traditional primary cells. A water battery is a battery that does not contain toxic electrolytes and is designed to produce no voltage until it is soaked in or filled with water. Therefore, in comparison with the traditional primary cells, water batteries can be easily stored since no chemical reaction will occur as long as they are not in contact with water. Furthermore, materials used for manufacturing water batteries are environmentally friendly, which means that when a water battery is discarded, the components of the water battery can be easily recycled and do not produce toxic substances.
However, existing water batteries have some disadvantages. For example, the life time of existing water batteries depends on whether the electrode materials of the batteries can be completely consumed during the chemical reaction between the electrode materials. The electrodes of existing water batteries are not designed to have an optimal exposure area for reaction. Furthermore, the used electrode materials of existing water batteries cannot be easily replaced with new electrode materials. Therefore, there is a need to develop a water-activated power generating device that overcomes the disadvantages mentioned above.